1. Field of the Invention
The present invention relates to a multi-point range measuring system for determining the distance of photographing based on range measuring information in plural directions, and more particularly to an automatic focusing device of a camera employing multi-point range measuring system.
2. Related Background Art
For the purpose of focusing to a main object without a cumbersome operation such as focus locking even when the main object is not positioned at the center of the field to be photographed, there is known a camera employing a multi-point range measuring system, in which range measurement is conducted on plural areas to obtain plural range information, and the photographing distance is determined from the range information. Japanese Patent Application Laid-open No. 59-143914 discloses an active type range measuring device in which there are defined plural range measuring areas uniformly distributed in a plane of a predetermined size perpendicular to the direction of distance, and light from plural light-emitting elements is time-sequentially directed to the plural range measuring areas to receive reflected light with a light-receiving element.
For the purpose of reducing the size of range measuring areas of the above-explained range measuring device and also reducing the size of the light emitting elements and light receiving elements thereof, there are already known the following devices.
U.S. Pat. Nos. 4,371,261, 4,534,636 and 4,575,211 disclosure a range measuring area g extended, as shown in FIG. 1, along a side of the photographing field and positioned at the center thereof, or a range measuring area h extended diagonally at the center of the photographing field as shown in FIG. 2. Also Japanese Patent Application Laid-open No. 61-246613 discloses a cross-shaped range measuring area i as shown in FIG. 3.
The arrangement and shape of such range measuring areas are devised to more securely catch the main object in the range measuring area, thereby reducing error in the range measurement for the main object. More specifically said arrangement and shape are selected because a higher probability of catching the main object is achieved by a range measurement in an area having a certain length in the vertical and/or horizontal direction of the photographing field, in comparison with the measurement at a point in the center of the field.
However such conventional range measuring areas have not been determined in consideration of the specific contour of persons as the object. Consequently, in photographing two persons for example, there may occur a case in which the range measuring area g or i is positioned between the faces of two persons as shown in FIGS. 1A and 3, so that the photograph is focused to the background. Also if the photographing field is selected vertically oblong and a person is positioned out of the center of the photographing field as shown in FIG. 1B, the laterally elongated range measuring area explained above becomes ineffective.
Also the diagonal range measuring area h may not cover the person if the person is displaced in an in appropriate direction from the center of the photographing field as shown in FIG. 2.
For determining a photographing distance from plural range information obtained from range measurements of plural areas, there are already known various systems, including:
a system of selecting, among plural range information, the range information of a closest object as the photographing distance;
a system of determining a weighted average range of the objects in the central area of the photographing field and determining the photographing distance from the average range; and
a system of controlling the lens position and the diaphragm aperture in such a manner that the closest object and the farthest object are contained in the depth of focus. With respect to the positional relationship of the objects in the photographing field, the main object is often distant considerably from the background object such as wall, woods or mountain in case of outdoor photographing such as in a park or in a sight-seeing spot, but, in indoor photographing such as in an ordinary house, the main object is often close to other surrounding objects such as a wall, window or small articles. Also the distance between the main object and the photographer is generally shorter indoors than outdoors.
However, in the conventional multi-point range measuring system, the photographing distance of the photographing lens is determined without distinction between the indoor and outdoor conditions, so that appropriate focusing is not always obtained.